Motor bucks slightly (long)

Thu Nov 12 10:28:53 PST 2009

I have not followed the post, so sorry if it have been mentioned, but the
symptoms could be a bad N75 valve or an untight dumpvalve. As far as I
remember it is the little black Bosch dumpvalve, there may be the culprit.

Claus

----- Original Message ----- 
From: "Brandon Rogers" <brogers at terrix.com>
To: "'melvin guyer'" <melguy1 at yahoo.com>; "'Mike Miller'" 
<mikemilr at blackfoot.net>; "'200 20v List'" <200q20v at audifans.com>
Sent: Thursday, November 12, 2009 6:01 PM
Subject: RE: Motor bucks slightly (long)

> Sounds like the exact same symptoms I have.  I will be swapping in a new
> and/or known good RPM sensor hopefully in the next day or two and will
> report back to the list.
>
> Brandon
>
> -----Original Message-----
> From: melvin guyer [mailto:melguy1 at yahoo.com]
> Sent: Wednesday, November 11, 2009 3:47 PM
> To: Mike Miller; Brandon Rogers; 200 20v List
> Subject: Re: Motor bucks slightly (long)
>
>
> there must be an epidemic of bucking 200q20v's. My 200 began bucking about
> two months ago. It feels like a momentary power loss and the "buck" is the
> sudden resumption of power. I have taken the car to the Audi dealer for
> diagnosis and repair and after lots of time and $$ it still bucks. 
> Typically
> it bucks two or three times within the first 10 minutes following a cold
> start. It bucks intermittently after that, both under acceleration and 
> while
> running at constant moderate speed. It also occasionally stalls now too,
> after hard acceleration and then a let up on the gas pedal. The idle
> stabilizer valve has been replaced and the O2 sensor as well, but that
> hasn't helped. The Audi dealer now suggests that the problem lies with the
> electronic engine control module(?). The car has 89k miles and is in
> excellent condition, always dealer maintained. Any ideas that come up on 
> how
> to fix this would be welcome.
>
> Thanks,
> Mel
>
> mel guyer
>
>
>
>  _____
>
> From: Mike Miller <mikemilr at blackfoot.net>
> To: Brandon Rogers <brogers at terrix.com>; 200 20v List 
> <200q20v at audifans.com>
> Sent: Wed, November 11, 2009 4:00:06 PM
> Subject: Re: Motor bucks slightly (long)
>
> Where is that located?
>
> I get the engine buck more so with engine warm than cold and more so in
> higher gears (4th 5th) than 1st thru 3rd. Boost has also dropped from 1.8 
> to
>
> 1.5 indicated. Most of the boost drop occured after replacing the lower 
> hose
>
> on the IM - the one the Bypass valve ties into - that section split. I've
> replaced bypass valve, MAF. plugs wires, and a few othere things. I've 
> been
> thinking IAT sensor - where si that located?
>
> mike miller
>
>
> ----- Original Message ----- 
> From: Brandon Rogers
> To: 'David Sexton'
> Cc: 200q20v at audifans.com
> Sent: Wednesday, November 11, 2009 1:32 PM
> Subject: RE: Motor bucks slightly (long)
>
>
> Oh Snap!!!!
>
> Duh - just recalled I did pull codes one more time with motor still 
> running
> (after last time I drove it when it bucked a lot when hot) - it did say
> "sporadic RPM sensor".
>
> Can't believe I forgot I did that!!!!!
>
> Now to swap in a known good.
>
> Thank you!
>
> Brandon
> I CC'd the list for archives sake
>
> -----Original Message-----
> From: David Sexton [mailto:sextondm at gmail.com]
> Sent: Wednesday, November 11, 2009 12:04 PM
> To: Brandon Rogers
> Subject: Re: Motor bucks slightly (long)
>
>
> Brandon,
> I had a similar experience with my '91 200 20V in the last few months. 
> The
> problem got worse until my car would buck and then stall, and not want to
> restart.
> Mine turned out to be the RPM Sensor going bad, and finally giving it up.
> But it was characterized by that "buck" like you described.  I didn't have
> any codes until the car finally wouldn't start.
> I ended up replacing the RPM Sensor and the Reference Sensor just for
> reliability sake.
> Good luck,
>
> Dave Sexton
>
>
>
> On Wed, Nov 11, 2009 at 9:41 AM, Brandon Rogers <brogers at terrix.com> 
> wrote:
>
>
> Guys-
> Experiencing a weird motor issue that has gotten worse in the last week.
> Really got me scratching my head.
>
> Over the last year or two my engine has bucked a little (on rare 
> occasions)
> when starting off.  This is when when the engine is cold (usually but NOT
> always) and fully in gear and already moving a few (maybe 5 tops?) mph - 
> not
> during clutch engagement - but right after.  A few days ago I was going to
> drive the car to work - backed out of the garage and the motor stalled 
> with
> car in neutral.  Re-started fine - but decided to take the S4 to work
> instead.  So that night I went out to the garage - no codes - started 
> fine -
> backed out - no stall.  But it did buck a couple minutes later - in the
> beginning when I took it for a spin.  It was a bigger buck compared to
> "normal".  These aren't bang your head on the steering wheel bucks but
> something is definitely going on.  Pulled codes again right away - 
> nothing.
> Drove around for 10 minutes - no more bucking.  Next day I decided to give
> it another go.  Pulled codes again JIC - nothing.  Car started fine and 
> all
> that - but it did buck once while cold when I pulled onto the street. 
> Then
> no more issues on the way in to work.  Continued to buck a little (say 
> once)
> within the first few minutes each tine I drove it.
>
> Something is going on with my engine - here are my observations:
>
> 1.  Bucks once or twice when cold at low rpm in 1st - goes away when 
> warm -
> more often in the last few days.  It _has_ done it more when warm in the
> last day or two.
> 2.  Very rich exhaust smell at idle - still
> 3.  Out of spec O2 Adaptation Values (I did put a new O2 sensor in - 
> however
> that is not a solution to out of spec adaptation per Bentley)
> 4.  Failed NOX emissions test - high NOX signals high exhaust temps (lean
> run?) (later passed - just just barely)
>
> As a side point to the data - I only get about 17 mpg - but I do likey the
> boost (this motor is in an ur-quattro)  so I don't consider that too
> much....
>
> So a few people suggested I pressure the system sounded like an air leak -
> and I do agree.  So I did (again - had done it a few times).
>
> So over the weekend I pressure tested the system - up to about 15 psi.
> There was a slight leak in the rubber connector hose from the metal
> crankcase breather (above the EM) to that black plastic thingie (TM) 
> behind
> the VC.
> Some air coming out the oil fill cap.
>
> So then I blocked the crankcase breather off.  No boost leaks in the 
> intake
> tract.  I used a stethoscope (hose) at all the junctions - can't miss an 
> air
> leak.
>
> But I kept looking around - decided to pull off the small vacuum lines 
> that
> come off the back of the IM and use the mighty vac.  The first one held no
> vacuum at all.  Well it turned out a hose had come off - but it was 
> _AFTER_
> a check valve - so no boost leak but was allowing incoming unmetered air
> under vacuum conditions - which really seemed like the type of problem I 
> was
> experiencing.  Fixed it.  Other two were tight - held vacuum.
>
> Unfortunately it did _not_ affect how the car ran. :-(((  Still had a 
> couple
> minor bucks when I drove the car in - then quite a few on the way home 
> when
> the engine was hot. Big disappointment.
>
> I will replace the crankcase breather section and see if that does the
> trick.
>
> Anybody else have this issue before???  Any other ideas?
>
> Brandon
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